In testing of ordnance firing circuits, extreme care must be taken to insure that the ordnance to be fired is not connected into a live firing circuit. This normally is accomplished by checking the firing circuit with a standard type voltmeter to insure that no signal voltage is present. While this method is adequate it is cumbersome, time consuming and in many cases can be subject to error depending on the skill of the operator, since to insure a properly operating meter it must first be checked. This is necessary since an inoperative meter may either fail to indicate the presence of a signal voltage or may introduce a signal voltage into the firing circuit. To properly check a standard meter requires that it first be compared with a known external signal source. Next, the meter is connected to the firing circuit, and operated from its high to low range in order to protect the meter and to insure that the minimum signal level required to detonate the ordnance is not present on the firing circuit prior to ordnance hookup. Finally, due to the design of most voltmeters only one polarity of DC or an AC signal may be measured in a given range setting. If this is the case it may then be discovered, when switching to the low ranges, that the polarity is reversed and the meter leads must be switched to determine if the minimum signal required for detonation is present.
In order to overcome these deficiencies it is desirable to have a meter circuitry which can be connected to an ordnance firing circuit and will detect and display the presence of any signal that can detonate the ordnance without regard to the polarity of the signal or without having to switch the meter range. In addition the meter incorporates a built-in test circuit to positively check the meter before its connection to the firing circuit to insure proper operation.